Washington D.C., New York and Chicago all have had temperatures nearly 20 degrees above normal this winter, reports CBS News correspondent Cynthia Bowers. Minneapolis and Philadelphia have enjoyed 27 straight days of above-average temperatures.
CBS News correspondent Sharon Alfonsi reports that the high temperatures have been messing with Mother Nature's calendar.
Birds are migrating south later, and some Southern birds have taken up residence in the North, permanently. Plants in Washington, D.C., are flowering four days earlier than they did 30 years ago, loggerhead turtles are coming ashore in Florida 10 days earlier than they did 20 years ago, and male frogs in New York begin mating season two weeks earlier than a century ago.
According to CBS Early Show meteorologist Dave Price, the warm weather can be attributed primarily to El Nino and a jet stream that is so far north that it is locking out the cold arctic air that usually sweeps into the U.S. from Canada.
The El Nino, which is abnormally warm water in the Pacific, "affects everything from winds to what kind of weather we will experience in different parts of the country," Price said.
He added that a Bermuda high, an area of high pressure of that forms over the Atlantic during hurricane season, has whipped up moisture and warm air toward the Northeast.
Meanwhile, British climate scientists predict that a resurgent El Nino climate trend combined with higher levels of greenhouse gases could touch off a fresh round of ecological disasters — and make 2007 the world's hottest year on record.
"Even a moderate (El Nino) warming event is enough to push the global temperatures over the top," said Phil Jones, director of the Climatic Research unit at the University of East Anglia.
The warmest year on record is 1998, when the average global temperature was 1.2 degrees Fahrenheit higher than the long-term average of 57 degrees. Though such a change appears small, incremental differences can, for example, add to the ferocity of storms by evaporating more steam off the ocean.
There is a 60 percent chance that the average global temperature for 2007 will match or break the record, Britain's Meteorological Office said Thursday. The consequences of the high temperatures could be felt worldwide.
While the warm winter temperatures won't garner many complaints from residents in the eastern half of the United States, heavy snowstorms in the Plains regions and tornadoes in the Southeast have caused major problems for thousands of Americans.
touching down during a strong cluster of storms in southern Louisiana, authorities said Thursday. And more than a week after a blizzard blasted Colorado, a .
While the effects of El Nino are varied and often volatile, they also can do some good. El Nino tends to take the punch out of the Atlantic hurricane season by generating crosswinds that can rip the storms apart — good news for Florida's orange growers, for example.
"The short-term effects of global warming on crop production are very uneven," said Daniel Hillel, a researcher at Columbia University's Center for Climate Systems Research. "I warn against making definitive predictions regarding any one season's weather."